We are requesting funds for the purchase of a state-of-the art fluorescence activated cell sorter (FACS), the BD Biosciences FACSAria II, to support research projects in the newly established Institute of Stem Cell Biology and Regenerative Medicine (ISCBRM) at Stanford University School of Medicine. The ISCBRM is expanding rapidly, with three new faculty members added in the last two years, and another two being added in 2009. FACS is the key platform technology for all aspects of the research at ISCBRM, including the identification, isolation, and characterization of highly purified subsets of stem and progenitor cells from normal tissues, and cancer stem cells from a wide variety of malignant tissues. Due to the rarity of the stem cell populations isolated in our FACS sorts, each sort routinely requires a minimum of two to four hours. In addition, most experiments require two sequential sorting runs to adequately remove contaminating cells. So individual experiments can require 4-8 hours of FACS sorting time. The increased staffing at ISCBRM, combined with the fact that all faculty members require long hours of FACS sorting of their cells of interest, has recently led to a bottleneck in terms of flow cytometry access, and this is significantly impeding scientific progress. Another consideration that further underscores our need for an additional FACS is that many projects at ISCBRM use human cancer tissues which are received at short notice, often with no more than a few hours to 1-2 days before sorting of the live cells must be executed. This situation requires a flow cytometry capacity with sufficient flexibility in scheduling and availability to accommodate samples at short notice. The intensive use of our current FACS facility makes it almost impossible to handle samples at short notice, and there have been many occasions when precious and rare clinical samples have been wasted. The following proposal lists the faculty members who need additional FACS access, and describes the projects in their labs that require extensive FACS sorting time. We are specifically requesting a BD Biosciences FACSAria II because each of the projects described herein requires multi-parameter sorting. In summary we have a pressing need to purchase a FACSAria II to relieve our current flow cytometry access bottleneck and thereby accelerate our progress in stem cell research, and to provide sufficient scheduling flexibility to be able to handle extremely valuable clinical samples at short notice.